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SRINIVASU ERALLA asked 6 months ago

What is primary thread in operating system?

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AdminAdmin answered 6 months ago

–> “threads” are units of execution within a process…a process contains at
least on thread(called main thread) which executes the “main() function in the
–> program may create more threads to accomplish multi-tasking inside a
–> all threads in a process , execute in parallel by getting their own time
slice from the “linux schedular”.
–> but in linux kernal, multiple threads in a single process, are the same as
the “multiple unrelated processes, which share the address space, open files
and other kernal resources….this process is implemented using “clone()
system call”.
–> when a process dies, all the threads in the process also dies.
–> “threads” in the process share all the resources except some hich makes
them schedule individually on the processor…it includes SP,IP,CPU registres,
scheduling proprties and TSD(thread specific data)..
–>threads are called “lightweight process” bcz they r not creating problem/
overhead in new process creation.
–> there is no child-parent relationship between threads….but thread creation
is allowed from any thread…
–> Multi threading is heavily used in GUI application for e.g we can have
“one thread which is handling user interface events” , other threads handling
corresponding data base for the user…
Threads Vs. Process :-
–>thread creation is many times faster than process creation…
–> “context switching of threads” is much faster than than “context switching
of process”
–> “Debugging of multi threaded program” is easier than that of “multiprocess”
program …..use gdb
–> “process” uses a lot of kernal memory , whereas threads uses less kernal
memory …
Note :- linux provides “pthreads API implementation for applications to create
and manage multiple threads within a process”…..IEEE standard 10003.1c or
POSIX=Portable Operating System Interface [for Unix].
Services offered by POSIX.1c are :-
1)thread creation,control,cleanup.
2)thread scheduling
3)thread synchronization
4)signal handling ….
Note :- Debugging a multi-threaded program is much harder than debugging a
single threaded programs due to “unpredictable nature of schedular in
scheduling threads on the processors.
Note :- Bugs in a multi-threaded application are hard to re-produce bcz they
occur only when they are scheduled in a particular manner , which is
hard to predict ..
Note :- Threads should use “only re-entrant functions” which are “threadsafe”
to ensure data integrity and unpredictable behaviour….for e.g “errno”
threads shares the address space of the process in which they are running
and have their own stack to run the thread function ….
pthread_create() :- function used for creating threads ….
int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg);
1st arg:- pthread-identifier which will be set to thread-identifer when the
thread is successfully created ..
2nd arg :- thread attribute object …
3rd arg :- ptr to function which takes void* as arguement and returns void*
4th arg :- ptr to arguemnt which shall be passed to start_routine
terminating a thread :- use pthread_exit() function …
void pthread_exit(void *retval);
is value returned from thread.
Note :- pthread_exit() function terminates the calling thread and makes the
value “retval” available to any successful join with terminating thread ..
Note :- after a thread is terminated , result of access to local varibale of thread
is undefined …
PTHREAD_JOIN() :- this function blocks the current thread until the thread
“thread” terminates ..
int pthread_join(pthread_t thread, void **value_ptr);
–> upon success, pthread_join() will return zero
–> pthread_join() function suspends the execution of calling threads until the
target thread terminates
Note :- value passed to “pthread_exit()” by terminating thread is made
available in location referenced by “last arguement of Pthread_join()”.

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